Age-hardenable, nickel-base superalloy with improved notch ductility

ABSTRACT

A precipitation hardenable nickel base alloy that provides a novel combination of elevated temperature strength, ductility, and reduced notch sensitivity at temperatures up to about 1300° F. is described. The alloy contains, in weight percent, about 
                                           Carbon   0.10   max.         Manganese   0.35   max.         Silicon   0.2-0.7         Phosphorus   0.03   max.         Sulfur   0.015   max.         Chromium   12-20         Molybdenum   4   max.         Tungsten   6   max.         Cobalt   5-12         Iron   14   max.         Titanium   0.4-1.4         Aluminum   0.6-2.6         Niobium   3-7         Boron   0.003-0.015                                            
the balance being nickel and usual impurities. An article made from the alloy and a method of making the alloy are also disclosed.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Patent Application No. 60/894,260, filed Mar. 12, 2007, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to nickel-base superalloys and in particular to a nickel-base superalloy in which the elements are balanced to provide a unique combination of strength and improved notch ductility, particularly at elevated temperatures up to about 1300° F.

BACKGROUND OF THE INVENTION

Waspaloy (UNS N07001) is a precipitation hardenable, nickel-base alloy which is used in elevated temperature applications. The alloy has found particular utility in gas turbine engine parts and aircraft jet engines that require considerable strength and good resistance to oxidation and hot corrosion at temperatures up to about 1600° F. (871° C.). Waspaloy provides good resistance to hot corrosion that results from exposure to combustion byproducts encountered in gas turbines and aircraft jet engines. A disadvantage of Waspaloy is that it is a relatively expensive alloy compared to other nickel-base superalloys. The higher cost of Waspaloy is attributable to the high amounts of nickel and cobalt used in the alloy and the difficulty of processing the alloy such as hot working and welding.

Alloy 718 (UNS N07718) is another precipitation hardenable nickel-base superalloy that provides very high yield strength, tensile strength, and creep rupture properties. However, the combination of properties provided by Alloy 718 degrades at very high temperatures. Therefore, the alloy is typically limited to applications that involve temperatures below about 1300° F. (704° C.).

A further precipitation hardenable nickel-base alloy designated UNS N07818 is known. That alloy has a composition that is designed to provide elevated temperature mechanical properties and processing characteristics that are intermediate to those provided by Waspaloy and 718. It has been determined that UNS N07818 can exhibit increased notch sensitivity during stress rupture testing at 1300° F. (704° C.) at higher stress levels of about 90 to 100 ksi. Notch sensitivity has been defined as the extent to which the sensitivity of a material to fracture is increased by the presence of a stress concentration area, such as notch, crack, or a scratch on the material. Higher notch sensitivity is usually associated with brittle materials, whereas lower notch sensitivity is usually associated with ductile materials. ASM Materials Engineering Dictionary, p. 294, ASM International 1992.

In view of the foregoing, it appears that there is a need for a precipitation hardenable, nickel-base alloy that provides the elevated temperature mechanical properties of UNS N07818, but with improved notch ductility at stress levels of 90 ksi and above.

SUMMARY OF THE INVENTION

The shortcomings of the alloys described above are overcome by an alloy and method of making an alloy in accordance with the present invention. In accordance with a first aspect of the present invention there is provided an alloy having the following weight percent composition.

Carbon 0-0.10 Manganese 0.35 Silicon 0.2-0.7 Phosphorus 0.03 max. Sulfur 0.015 max. Chromium 12-20 Molybdenum 4 max. Tungsten 6 max. Cobalt 5-12 Iron 14 max. Titanium 0.4-1.4 Aluminum 0.6-2.6 Niobium 3-7 Boron 0.003-0.015

The balance of the alloy is nickel and usual impurities. The alloy of this invention provides a novel combination of elevated temperature strength, ductility, and reduced notch sensitivity relative to UNS N07818.

In accordance with another aspect of the present invention, there is provided a method of making a precipitation hardenable nickel base superalloy. The method according to the invention includes the step of providing charge materials in a vacuum melting furnace, the charge materials being selected to provide an alloy having the following weight percent composition.

Carbon up to about 0.10 Manganese up to about 0.35 Phosphorus 0.03 max. Sulfur 0.015 max. Chromium 12-20 Molybdenum 4 max. Tungsten 6 max. Cobalt 5-12 Iron 14 max. Titanium 0.4-1.4 Aluminum 0.6-2.6 Niobium 4-8 Boron 0.003-0.015 Nickel and Impurities Balance

In a second step, the process includes adding an amount of silicon that is effective to provide precipitation of a globular intermetallic phase in the alloy during elevated temperature processing of the alloy. Preferably, that objective is obtained when a retained amount of about 0.2 to 0.7 weight percent silicon is present in the alloy after melting and casting.

In accordance with a further aspect of this invention there is provided an article of manufacture formed of a precipitation hardenable nickel base alloy. The article has a matrix formed of a nickel base alloy, a strengthening precipitate dispersed in the matrix material, and a globular intermetallic precipitate dispersed at the grain boundaries of the matrix material.

Here and throughout this specification, the term “percent” or the symbol “%” means percent by weight, unless otherwise indicated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are scanning electron micrographs (SEM) of a sample of Heat 10932 taken at magnifications 1000X and 5000X, respectively;

FIG. 2 shows Larson-Miller graphs of stress rupture strength for Heat 10931, Heat 10932, Alloy 718, and WASPALOY;

FIG. 3A shows graphs of room temperature tensile and yield strength properties of Heats 10931 and 10932 after exposure for up to 10,000 hours at 1300° F.;

FIG. 3B shows graphs of room temperature tensile ductility properties of Heats 10931 and 10932 after exposure for up to 10,000 hours at 1300° F.;

FIG. 4A shows graphs of 1300° F. tensile and yield strength properties of Heats 10931 and 10932 after exposure for up to 10,000 hours at 1300° F.;

FIG. 4B shows graphs of 1300° F. tensile ductility properties of Heats 10931 and 10932 after exposure for up to 10,000 hours at 1300° F.;

FIG. 5A shows graphs for 1300° F. stress-rupture life of Heats 10931 and 10932 after exposure for up to 10,000 hours at 1300° F.;

FIG. 5B shows graphs for 1300° F. stress-rupture ductility of Heats 10931 and 10932 after exposure for up to 10,000 hours at 1300° F.

DETAILED DESCRIPTION

The present invention stems from the inventors' discovery that a Laves-type secondary phase can be beneficial to improve the notch ductility of a low-cobalt-containing, precipitation-hardenable, nickel base superalloy such as Alloy 718. The Laves phase that is beneficial in the present invention is an intermetallic phase containing one or more of the elements Si, Fe, Ni, Co, and Cr, in combination with one or more of the elements Nb, Mo, W, Al, and Ti. The beneficial Laves phase preferably forms at the grain boundaries of the matrix material. The Laves phase of interest in alloy of this invention is readily distinguishable from the strengthening phases which form during the age hardening heat treatment. Those phases are usually gamma prime (γ′) and gamma double-prime (γ″). The Laves phase used in the present invention is believed to have a globular morphology and is also distinguishable from the blocky form of Laves phase that forms during solidification. This secondary phase aids grain refinement during processing of the alloy and appears to contribute to retention of a fine grain structure when the alloy is processed at a solution temperature higher than those typically used for alloys such as Alloy 718.

An alloy made in accordance with the present invention is a nickel base, superalloy that includes up to about 0.10% carbon, up to about 0.35% manganese, not more than about 0.03% phosphorus, not more than about 0.015% sulfur, about 12-20% chromium, not more than about 4% molybdenum, not more than about 6% tungsten, about 5-12% cobalt, not more than about 14% iron, about 0.4-1.4% titanium, about 0.6-2.6% aluminum, about 4-8% niobium, about 0.003-0.015% boron. The alloy also contains a positive addition of silicon effective to provide a retained amount of about 0.2-0.7% silicon. Preferably the alloy contains at least about 0.3% silicon and not more than about 0.6% silicon. For best results, the alloy contains about 0.4-0.5% silicon. The balance of the alloy is nickel and the usual impurities present in commercial grades of nickel base superalloys.

WORKING EXAMPLES Example I

A globular Laves phase forms in nickel-cobalt-base, low thermal expansion superalloys at silicon levels less than about 0.5%. However, a positive addition of silicon in that range was not previously used in nickel base superalloys such as 718 or UNS N07818. Therefore, it was decided to evaluate the effect of silicon in the range 0 to 1.5%. More specifically, four silicon levels were selected for evaluation, about 0%, about 0.5%, about 1.0%, and about 1.5% silicon. The silicon was added to a base alloy composition for UNS N07818. Niobium is known to stabilize the globular Laves phase in the low thermal expansion superalloys. Accordingly, it was decided to test experimental alloy compositions containing each of those four silicon levels in combination with about 6.0% niobium and also with about 5.4% niobium. The latter niobium amount is closer to the nominal niobium content of 718 and UNS N07818.

Eight 22-lb heats were vacuum-induction melted and cast as 2.75″ square, tapered ingots. The weight percent chemistries of those heats are shown Table I (Series I heats). The ingots were homogenized and then heated to 2050° F. for forging. The ingots were forged to 1⅜″ square, reheated to 2050° F., and then finish forged to ¾″×1¼″ bar. One bar from heat 1101 broke during forging because it was bent and it was forged at too low a temperature. Otherwise, there were no hot working problems that could be attributed to the modified compositions. The alloy according to this invention forges similarly to Alloy 718 with respect to start and finish temperatures and the applied forging force.

The solution heat treating range for the experimental alloys was initially selected to be about 1750° F. to about 1850° F., but it was found that notch sensitivity increased when the alloys were solution treated in the upper part of the temperature range, i.e., from about 1800° F. to about 1850° F. Solution treatments at 1800° F. and 1850° F. for 1 hour, followed by cooling in air, were used for the evaluations. The solution treated ingots were given a double aging treatment consisting of heating at 1450° F. for 8 hours, furnace cooling at a rate of 100° F. per hour to 1300° F., holding at 1300° F. for 8 hours, and then cooling in air.

Longitudinal mechanical test blanks were cut from a mid-radius section of the ¾″×1¼″ bars, two per section. The test blanks were heat treated as described above, one set with the 1800° F. solution treatment and a second set with the 1850° F. solution treatment. The heat treated blanks were then low-stress-ground. Tensile specimens having a 0.250″ gage diameter and stress-rupture specimens having a 0.178″ diameter were machined from the blanks. Tensile specimens representing both solution heat treatments were tested at room temperature and at 1300° F. The combination smooth-notched stress-rupture specimens were tested at 1300° F. at a stress level of 90 ksi. Because an 1850° F. treatment is known to increase notch sensitivity in other alloys, smooth section specimens were also tested to evaluate rupture ductility. It is not possible to measure ductility with a notched specimen. Stress-rupture properties were evaluated in this work because it is believed that there is a correlation between notch ductility and dwell crack growth resistance.

The results of the tensile and stress rupture testing for the eight Series I heats are shown in Table II. Microstructural observations of the test specimens are set forth in Table III. The microstructural observations make it clear that a globular Laves-type phase did precipitate in heats containing at least 0.5% silicon. The stress-rupture results for the Series I heats also indicate that heats with 0.5% Si or less, for example, Heat 1098, could provide improved notch ductility relative to UNS N07818.

Example II

Based on the results provided by the Series I heats, a second series of five heats was melted. One set contained about 0% silicon, another set contained about 0.15% silicon, a third set contained about 0.30% silicon, and the fourth set contained about 0.45% silicon. The weight percent compositions of the Series II heats are also shown in Table I. Because the first series of heats exhibited some segregation and nonuniform grain structures, certain processing changes were made. More specifically, the ingot size was increased from 2.75″ to 3.5″ so that the amount of reduction the ingots would undergo during processing would increase. In the second step of the homogenization treatment, the temperature was increased to reduce microsegregation in the alloy. The forging starting temperature was increased from 2050° F. to 2100° F. to avoid development of coarse unrecrystallized grains during forging of small section sizes. The finish width of the as-forged ingots was increased from 1.25″ to 1.375″ to shift the forging X-pattern away from the mid-radius region used to obtain material for test samples. Tensile and stress rupture samples were prepared and tested in the same manner as the Series I specimens, except as noted above. Test results for the five Series II heats are shown in Table IV. Microstructural observations for the Series II specimens are set forth in Table V.

It was found that the globular, Laves-type, secondary phase precipitated in the test alloys having a composition that includes at least about 0.3% silicon. More extensive amounts were observed in heats containing 0.42% silicon and above. The secondary phase restricted grain growth in the 1850° F. solution treated heats such that heats with 0.4% or more silicon had a very fine grain structure (ASTM 10 or finer). In contrast, UNS N07718 and UNS N07818 typically have medium grain sizes of ASTM 5-7 when solution treated at 1850° F. Clean microstructures with medium-to-coarse grain size are inherently susceptible to notch failures because of the rapid growth of grain boundary cracks.

Regardless of solution or test temperature, test heats containing the higher amounts of silicon (≧0.3%) provided increased yield strength and reduced tensile ductility compared to heats containing the lower amounts of silicon (<0.3%). The largest effects occurred in the heats containing positive amounts up to 0.5% Si where the globular Laves-type phase was observed to significantly reduce grain size. Further improvements in tensile properties with silicon above 0.5% were minor because all heats had ultra-fine grain size and very extensive fine precipitation of the globular Laves-type phase. The test results also show the effect of higher niobium content, i.e., 6% compared to 5.4%. The heats containing the higher amounts of niobium also provided higher strength, but somewhat reduced ductility. However, the effect was less pronounced than observed when only the amount of silicon is considered.

An important objective of the testing was to identify compositions with improved resistance to notch failures in stress-rupture tests. As can be seen from Tables II and IV of the Series I heats (0-1.6% Si), the heat with 0.5% Si and 5.4% Nb were free of notch failures. A similar result was observed during testing of Series II heats (0-0.45% Si) in that the heat with 0.42% Si and 5.4% Nb did not have notch failures. In general, increasing the amount of silicon generally resulted in reduced stress-rupture life. Effects on stress-rupture ductility were inconsistent. However, most specimens that fractured in the smooth section had high values for elongation and reduction of area. Although increasing the silicon content reduced stress-rupture life, the rupture lives for the heats containing 0.4-0.5% silicon are still comparable to those expected for Waspaloy under the same test conditions (1300° F. and 90 ksi).

Example III

Two 400-lb heats, one representing UNS N07818 (Heat 10931) and the other representing the alloy according to the present invention (Heat 10932), were VIM/VAR melted and cast as 8″ round ingots. Table VI shows the chemical analyses of the two heats. The ingots were homogenized and heated to about 2050° F. for forging. The ingots were forged to 6″ octagon billets in one heating. The 6″ octagonal billets were surface ground and then rotary forged to 2.8″ round bar from a starting temperature of about 1950° F. The billets were forged using five reductions of 20-22%. The applied forging forces were similar to those used for Alloy 718. The billet ends were cropped and samples from the croppings were macro-etch inspected. The inspection revealed no undesirable conditions.

Longitudinal mechanical test blanks were cut from the mid-radius location of the bars, six pieces per section. Based on previous results, solution treatments of 1800° F. to 1850° F. for 1 hour, followed by air cooling, were used to solution treat the test samples for evaluation of mechanical properties. The solution treatments were followed by a double-aging treatment of 1450° F. for 8 hours, furnace cooling at 100° F. per hour to 1300° F., holding at 1300° F. for 8 hours and then cooling in air. A first set of test blanks were cut before heat treatment. Some full sections were heat treated and then test blanks were cut after heat treatment to obtain samples that simulate the slower heating rate of larger section sizes.

Low-stress-ground 0.250″ gage diameter smooth tensile and 0.178″ diameter combination smooth-notched stress-rupture specimens were prepared from the test blanks. The tensile specimens representing the various solution temperatures were tested at room temperature and at 1300° F. The stress rupture specimens were tested at 1300° F./90 ksi. A few specimens were also tested at a higher stress level, 1300° F./100 ksi. Mechanical property results for the two heats are set forth in Table VII.

In order to determine the effects of long-term exposure at high service temperatures, fully-treated bar samples were exposed in air at 1300° F. for periods of up to 1,000, up to 3,000 hours, and up to 10,000 hours. Tensile and stress-rupture specimens were cut, machined, and tested as described above. Charpy V-notch (CVN) impact specimens were also prepared and tested. Table VIII shows the results of mechanical testing for the long-term exposed samples.

The globular second phase in heat-treated samples of the Heat 10932 was analyzed using SEM/EDS, EMPA (microprobe), and X-ray diffraction techniques. The phase was too fine to accurately analyze in situ. However, it was possible to confirm that the phase particles are enriched in Si, Nb, and Mo and depleted in Ni and Al relative to the matrix material. The phase material was isolated using carbon replicas and acid extraction. The X-ray diffraction analysis showed that there were matches with up to four Laves-type phases, two with hexagonal crystal structures and two with cubic structures. The basic formulas for the most likely matches are Co₃SiNb₂, Co₂Nb, and (Cr,Si,Fe)₂(Ti,Mo). The SEM/EDS analysis yielded the following quantitative analysis of the globular phase.

Element Wt. % At. % Cr 9.13 12.05 Fe 4.27 5.25 Co 8.22 9.57 Ni 20.03 23.42 Si 3.72 9.09 Ti 0.38 0.55 Al 0.26 0.65 Mo 19.62 14.04 Nb 34.36 25.38

FIGS. 1A and 1B show SEM micrographs of the grain boundary precipitates in a fully-treated sample of the Heat 10932. Samples of each heat were also analyzed (SEM/EDS) after 3,000-hour exposure at 1300° F. There were no additional phases found in Heat 10932 beyond the globular Laves-type phase. Heat 10931 contained small amounts of a phase with three possible matches, Fe-Mo (R-phase), Fe-Ti (Laves) and Ni-Mo.

The stress-rupture results listed in Table VII clearly confirm that the alloy Heat 10932 provides improved notch ductility for material solution treated at 1800-1850° F. prior to aging. For the known alloy, represented by Heat 10931 solution treated above 1800° F., 12 of 13 specimens had short-time notch failures at 1300° F./90-100 ksi. Thus, the alloy according to the present invention permits an extended solution treating range up to at least 1830° F. Heat 10932 did provide somewhat reduced stress-rupture life relative to Heat 10931. However, it is believed that the precipitation of fine Laves phase on the grain boundaries and finer grain size are responsible for the better notch ductility provided by Heat 10932. FIG. 2 shows Larson-Miller curves for the stress-rupture life performance of Heats 10931 and 10932 and for Alloy 718 and Waspaloy. The graphs shown in FIG. 2 indicate that the alloy according to this invention (Heat 10932) provides stress rupture life that is similar to or greater than that provided by the Waspaloy alloy.

Samples from both heats fractured in the notch region when solution treated at the higher temperature of 1850° F. prior to aging. Therefore, it appears that a temperature of 1850° F. represents the upper limit for a viable solution heat treatment for the tested alloys. The results presented in Table VII show that Heat 10932 provides significantly higher tensile strength than Heat 10931 although at somewhat reduced ductility. In the heat-treated condition, the material from Heat 10932 had finer grain size and more strain than the material from Heat 10931 (see Table VIII) which resulted in the strength improvement. FIGS. 3A and 3B show that the room-temperature tensile properties of both heats were relatively stable during 1300° F. exposure for up to 10,000 hours. Ductility was reduced somewhat, but neither alloy was embrittled. This result was particularly unexpected for Heat 10932, the higher Si-containing heat, because silicon is known to promote the formation of deleterious phases in other alloys after long-term exposure to elevated temperatures.

FIGS. 4A and 4B show that the 1300° F. tensile properties actually increased during long-term exposure. FIGS. 5A and 5B show that the stress-rupture life and ductility of the tested heats were stable alter the long-term exposure and that the notch ductility was not adversely affected. Both heats had reduced impact toughness alter long-term exposure (3,000 hours). Heat 10932 provided somewhat lower toughness, i.e., below about 10 ft-lbs, after the 1,000 hour and the 3,000 hour exposures. The fine globular phases did not embrittle these compositions for exposure times up to 3,000 hours. Rupture ductility increased with longer exposure and notch ductility was retained. Both compositions provided similar ductility after 10,000 hours at 1300° F.

It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It is understood, therefore, that the invention is not limited to the particular embodiments that are described, but is intended to cover all modifications and changes within the scope and spirit of the invention as described above and set forth in the appended claims.

TABLE I Chemical Compositions (Wt %) Heat C Mn Si P S Cr Ni Mo W Co Al Ti Nb B Ca Mg Fe Series I Heats (0 to 1.5% Si) 1096 0.021 0.05 <0.01 0.006 <0.0005 17.91 51.79 2.71 1.05 9.14 1.44 0.74 5.37 0.0048 0.001 0.002 9.79 1097 0.020 0.05 <0.01 <0.005 <0.0005 17.92 51.79 2.69 1.05 9.16 1.43 0.75 5.97 0.0050 0.001 0.002 9.20 1098 0.021 0.05 0.51 <0.005 <0.0005 17.89 51.80 2.72 1.05 9.15 1.41 0.75 5.39 0.0049 0.001 0.002 9.28 1099 0.026 0.05 0.52 <0.005 <0.0005 17.92 51.84 2.70 1.05 9.14 1.42 0.74 5.94 0.0053 0.001 0.002 8.67 1100 0.022 0.05 0.92 <0.005 <0.0005 17.96 51.82 2.71 1.06 9.14 1.43 0.75 5.37 0.0054 0.001 0.002 8.79 1101 0.030 0.05 1.03 <0.005 <0.0005 17.95 51.81 2.70 1.04 9.13 1.39 0.74 5.97 0.0057 0.001 0.002 8.18 1102 0.032 0.05 1.62 <0.005 <0.0005 17.93 51.72 2.71 1.04 9.13 1.41 0.74 5.40 0.0059 0.001 0.003 8.24 1103 0.032 0.05 1.57 <0.005 <0.0005 17.94 51.77 2.71 1.03 9.13 1.39 0.74 5.98 0.0055 0.001 0.002 7.68 Series II Heats (0 to 0.4% Si) 1227 0.024 0.05 <0.01 <0.005 <0.0005 17.90 51.84 2.70 1.01 9.08 1.45 0.74 5.40 0.0027 <0.001 0.003 9.82 1228 0.028 0.05 0.15 <0.005 <0.0005 17.94 51.75 2.70 1.02 9.10 1.44 0.74 5.42 0.0026 <0.001 0.002 9.69 1229 0.032 0.05 0.29 <0.005 <0.0005 17.93 51.80 2.70 1.02 9.09 1.46 0.74 5.40 0.0022 0.001 0.003 9.52 1230 0.028 0.05 0.29 <0.005 <0.0005 17.93 51.77 2.70 1.01 9.08 1.47 0.75 6.01 0.0037 0.001 0.003 8.94 1231 0.030 0.05 0.42 <0.005 <0.0005 17.98 51.72 2.70 1.02 9.09 1.46 0.74 5.43 0.0037 0.001 0.002 9.38

TABLE II Mechanical Properties - Series I Heats Room-Temperature Tensile 1300° F. Tensile Stress Rupture at 1300° F./90 ksi 0.2% 0.2% Elong Solution YS UTS Elong RA YS UTS Elong RA Time (%- RA Sample Heat Si Cb Temp (ksi) (ksi) (%-4D) (%) (ksi) (ksi) (%-4D) (%) (hrs) 4D) (%) Type 1096 <0.01 5.37 1800° F. 144 208 19 27 125 163 12 17 135 47.3 64.0 Combo 1800° F. 150 216 25 35 126 162 12 17 0.0 Notch Break Combo 1850° F. 134 202 26 45 115 158 11 18 128.2 34.0 55.6 Smooth 1850° F. 0.3 Notch Break Combo 1097 <0.01 5.97 1800° F. 165 201 5 12 139 166 20 15 0.2 Notch Break Combo 1800° F. 169 223 20 25 127 165 23 15 23.0 30.7 71.1 Combo 1850° F. 149 214 27 11 118 150   4**    13.4** 163.0 35.0 49.6 Smooth 1850° F. 0.1 Notch Break Combo 1098 0.51 5.39 1800° F. 171 222 15 20 143 167 11 17 34.8 14.7 20.9 Combo 1800° F. 165 213 9 14 133 163    5.9*    9.9* 29.2 18.9 21.9 Combo 1850° F. 170 223 26 21 143 159    3.9**    5.5** 34.5 34.0 70.0 Smooth 1850° F. 18.6 13.2 17.5 Combo 1099 0.52 5.94 1800° F. 196 230 4.7* 9.3* 149 169 11 14 23.7 33.8 67.2 Combo 1800° F. 187 233 9 9 146 171  8 14 0.0 Notch Break Combo 1850° F. 194 232 6 11 146 168  8 11 21.5 >10.5* 32.2 Smooth 1850° F. 14.6 21.7 26.3 Combo 1100 0.92 5.37 1800° F. 182 229 11 15 149 162   8.4   13.8 11.9 46.0 66.5 Combo 1800° F. 180 216 6 11 148 162   12.1   14.6 0.1 Notch Break Combo 1850° F. 176 212 6 12 144 165   10.7   11.3 11.0 >9.0* >9.0* Smooth 1850° F. 0.5 Notch Break Combo 1101 1.03 5.97 1800° F. 188 215 5 7 151 168   5.1   8.5 0.1 Notch Break Combo 1800° F. 193 226 10 14 149 166   7.4   11.2 15.8 42.6 66.1 Combo 1850° F. 184 223 8 14 151 171   7.6   10.7 5.9 5.8 9.1 Smooth 1850° F. 0.0 Notch Break Combo 1102 1.62 5.40 1800° F. 180 219 6 8 141 152 21 24 4.5 24.2 48.1 Combo 1800° F. 174 220 9 12 136 152 22 26 2.9 36.2 59.4 Combo 1850° F. 175 198 4 5 139 159  9 10 5.0 11.1 8.8 Smooth 1850° F. 6.1 50.8 64.6 Combo V001103 1.57 5.98 1800° F. 182 218 6 10 134 160   10.9   12.2 12.1 39.9 62.7 Combo 1800° F. 188 209 1.3* 3.5* 140 158   7.2   9.9 6.2 45.5 61.6 Combo 1850° F. 169 213 6.1* 10.6* 138 163   5.6   7.6 8.7 >16.2* 54.3 Smooth 1850° F. 0.0 Notch Break Combo * = broke in outer portion of gage section; ductility may not be representative ** = broke outside gage section; ductility values are invalid Heat Treatment: 1800° F. or 1850° F./1 h/AC + 1450° F./8 h/FC to 1300° F./8 h/AC Specimens: Tensile - 0.250″ gage diameter threaded, low-stress ground Stress Rupture - 0.178″ diameter combination smooth and notched (Kt = 3.9), low-stress ground

TABLE III Microstructural Observations for Series I Heats Solution Microstructural Observations Heat Si Cb Temp Grain Structure Precipitation 1096 <0.01 5.37 1800° F. Very fine, some Extensive fine delta recrystallized except in patches patches 1850° F. Recrystallized Little or none ASTM 6-7 1097 <0.01 5.97 1800° F. Recrystallized Extensive fine delta ASTM 3-5 with except in patches fine necklace 1850° F. Recrystallized Small amount of ASTM 5-7 grain boundary ppt 1098 0.51 5.39 1800° F. Very fine mixed Globular ppt with ASTM 7-8 throughout patches 1850° F. Mixed very fine Globular ppt and ASTM 5-7 throughout, less than 1800° F. 1099 0.52 5.94 1800° F. Very fine, some Globular ppt ASTM 7-8 urg throughout patches 1850° F. Mixed Globular ppt throughout 1100 0.92 5.37 1800° F. Uniform very fine Extensive ppt of various sizes 1850° F. Uniform very fine Extensive ppt of various sizes 1101 1.03 5.97 1800° F. Uniform very fine Very extensive ppt of various sizes 1850° F. Uniform very fine Very extensive ppt of various sizes 1102 1.62 5.40 1800° F. Uniform very fine Very extensive ppt of various sizes 1850° F. Uniform very fine Very extensive ppt of various sizes 1103 1.57 5.98 1800° F. Uniform very fine Very extensive ppt of various sizes 1850° F. Uniform very fine Very extensive ppt of various sizes Heat Treatment: 1800° F. or 1850° F./1 h/AC + 1450° F./8 h/FC to 1300° F./8 h/AC

TABLE IV Mechanical Properties of Series II Heats Room-Temperature Tensile 1300° F. Tensile Stress Rupture at 1300° F./90 ksi 0.2% 0.2% Elong Solution YS UTS Elong RA YS UTS Elong RA Time (%- RA Sample Heat Si Cb Temp (ksi) (ksi) (%-4D) (%) (ksi) (ksi) (%-4D) (%) (hrs) 4D) (%) Type 1227 <0.01 5.40 1800° F. 172 222 18 27 138 166 22 44 46.5 29.9 69.9 Combo 1800° F. 159 216 25 45 135 165 14 15 49.4 26.4* 72.0 Combo 1850° F. 140 207 28 50 116 157 10 12 0.1 Notch Break Combo 1850° F. 140 207 27 51 117 157 ** ** 128.5 48.3 26.4 Combo 1228 0.15 5.42 1800° F. 161 219 24 46 139 166 16 20 26.7 36.1 69.8 Combo 1800° F. 160 218 23 45 136 166 20 29 21.7 35.8 70.1 Combo 1850° F. 137 208 28 48 114 159 11 14 0.2 Notch Break Combo 1850° F. 139 207 28 48 120 160 10 17 0.2 Notch Break Combo 1229 0.29 5.40 1800° F. 171 224 19 29 142 166 14 17 32.5 51.7 65.8 Combo 1800° F. 169 222 21 40 138 164 10 12 33.2 37.9* 50.7* Combo 1850° F. 152 214  23*  45* 130 165 10 15 65.5 21.9 36.2 Combo 1850° F. 149 212 26 48 122 159 11 12 0.2 Notch Break Combo 1230 0.29 6.01 1800° F. 177 228 17 28 143 168 16 26 49.2 37.4 60.2 Combo 1800° F. 174 227 15 22 141 168 20 25 30.2 39.9 71.3 Combo 1850° F. 170 226 22 38 145 172 9 11 36.2 11.0* 19.4* Combo 1850° F. 176 229 21 38 147 173 8 12 39.0 32.0 65.9 Combo 1231 0.42 5.43 1800° F. 169 223 18 34 141 166 11.3 15.0 49.5 40.9 58.2 Combo 1800° F. 172 225 20 36 147 168 11.4 15.2 28.5 17.8 23.1 Combo 1850° F. 166 222 20 36 140 167 10 14 43.6 39.9 69.6 Combo 1850° F. 160 217 21 39 142 165 12.5 12.7 72.8 13.8* 46.2* Combo * = broke in outer portion of gage section; ductility may not be representative ** = broke outside gage section; ductility values are invalid Heat Treatment: 1800° F. or 1850° F./1 h/AC + 1450° F./8 h/FC to 1300° F./8 h/AC Specimens: Tensile - 0.250″ gage diameter threaded, low-stress ground Stress Rupture - 0.178″ diameter combination smooth and notched (Kt = 3.9), low-stress ground

TABLE V Microstructural Observations for Series II Heats Solution Microstructural Observations Heat Si Cb Temp Grain Structure Precipitation 1227 <0.01 5.40 1800° F. Mixed ASTM Extensive fine delta 10-11 with 6-7 in fine grains 1800° F. Mostly fine Extensive fine delta ASTM 10-11 in fine grains 1850° F. Uniform Little or no recrystallized 6-7 precipitation 1850° F. Uniform Little or no recrystallized 5-7 precipitation 1228 0.15 5.42 1800° F. Mixed ASTM Moderate matrix 9-10, some 6-7 delta only in fines 1800° F. Mostly fine Moderate matrix ASTM 9-10 delta 1850° F. Recrystallized Little or no ASTM 5-7 precipitation 1850° F. Recrystallized Little or no ASTM 4-7 precipitation 1229 0.29 5.40 1800° F. Mostly ASTM Extensive, more 10-11, some 6-8 globular ppt. 1800° F. Necklace struc- Mixed, small to ture of 6-7 and 11 large amount of ppt. 1850° F. Recrystallized, Mixed, small to mixed ASTM 5-8 moderate amount of ppt. 1850° F. Recrystallized Small amount of ASTM 5-7 grain boundary ppt. 1230 0.29 6.01 1800° F. Necklace Moderate to very structure ASTM extensive ppt. 6-7 with 12 1800° F. Necklace Moderate to very structure ASTM extensive ppt. 6-7 with 12 1850° F. Mixed ASTM Extensive globular 6-7 and 10-11 ppt. 1850° F. Mostly ASTM Extensive globular 10-11, some 6-7 ppt. 1231 0.42 5.43 1800° F. Fine ASTM Extensive globular 10-12, some ppt. necklace 1800° F. Fine ASTM Extensive globular 11-12, some 6-8 ppt. 1850° F. Mostly fine Extensive globular ASTM 11-12 ppt. 1850° F. Mixed ASTM Extensive globular 11-12, some 6-8 ppt. Heat Treatment: 1800° F. or 1850° F./1 h/AC + 1450° F./8 h/FC to 1300° F./8 h/AC

TABLE VI Chemical Compositions of Test Heats (Wt %) Heat C Mn Si P S Cr Ni Mo W Co Al Ti Nb B Ca Mg Fe 10931 0.025 0.05 0.05 0.007 <0.0005 17.83 51.56 2.66 1.05 9.08 1.45 0.74 5.31 0.0051 <0.001 0.003 10.19 10932 0.027 0.05 0.39 0.006 <0.0005 17.97 51.87 2.70 1.00 9.07 1.46 0.74 5.34 0.0051 <0.001 0.003 9.33

TABLE VII Mechanical Properties Room-Temperature Stress Rupture- Stress Rupture- Tensile 1300° F. Tensile 1300° F./90 ksi 1300° F./100 ksi Solution Sample 0.2% 0.2% Elong Elong Temp Loca- YS UTS Elong RA YS UTS Elong RA Time (%- RA Time (%- RA Heat % Si (1 h/AC) tion (ksi) (ksi) (%-4D) (%) (ksi) (ksi) (%-4D) (%) (hrs) 4D) (%) (hrs) 4D) (%) 10931 0.05 1800° F. Mid- 141 202 25 47 121 151  7*  15* 164.7 27.5 38.5 Radius Mid- 143 205 48 126 159 **  16* 145.6 32.7 49.9 Radius Center 0.1 Notch Break 1815° F. Mid- 141 203 24 46 119 159 12 14 19.5 Notch Break 0.3 Notch Break Radius Mid- 0.2 Notch Break Radius Center 144 204  24*  45* 1830° F. Mid- 134 202 32 46 116 157  10*  12* 0.0 Notch Break 0.2 Notch Break Radius Mid- 0.1 Notch Break 0.2 Notch Break Radius Center 130 201 32 42 1850° F. Mid- 130 198 33 47 110 147 11 17 0.2 Notch Break Radius Mid- 130 198 33 48 112 147 11 17 0.2 Notch Break Radius *** Mid- 135 202 31 46 116 157 11 13 0.2 Notch Break Radius *** Mid- 134 202 32 46 0.2 Notch Break Radius *** Mid- 150.8 29.7 31.2 Radius Center 0.0 Notch Break 10932 0.39 1800° F. Mid- 177 217 22 36 146 168  6  7 86.0 27.9 38.8 Radius Mid- 141 217 22 36 124 161  7 11 83.5 ** ** Radius Center 33.3 25.9 27.1 1815° F. Mid- 151 211 26 36 128 165 10 11 91.2 18.1 17.8 26.9 19.9 18.4 Radius Mid- 85.7 35.5 38.5 34.7 16.5** 14.5** Radius Center 166 214 26 34 1830° F. Mid- 149 210 23 39 123 160 10 10 81.2 29.6 29.1 27.0 15.4** 16.1** Radius Mid- 89.3 30.1 31.3 0.2 Notch Break Radius Center 157 212  22*  36* 1850° F. Mid- 139 208 29 42 117 156  8 14 0.0 Notch Break Radius Mid- 141 208 29 41 120 158  7 12 0.0 Notch Break Radius *** Mid- 143 210 28 38 121 161 11 15 96.6 23.1 23.8 Radius *** Mid- 143 209 27 38 0.1 Notch Break Radius *** Mid- 0.1 Notch Break Radius Center 0.0 Notch Break * = broke in outer portion of gage section; ductility may not be representative ** = broke at gage mark; ductility values are not valid *** = heat treated as full section rather than as small bank

TABLE VIII Effects of Long-Term 1300° F. Exposure on Mechanical Properties Charpy Stress Rupture at Room-Temperature Tensile V-Notch 1300° F. Tensile 1300° F./90 ksi 1300° F. Sample 0.2% Impact 0.2% Elong Exposure Loca- YS UTS Elong RA Energy YS UTS Elong RA Time (%- RA Heat % Si (hours) tion (ksi) (ksi) (%-4D) (%) (ft-lbs) (ksi) (ksi) (%-4D) (%) (hrs) 4D) (%) 10931 0.05 0 Mid- 141 202 25 47 121 151  7*  15* 164.7 27.5  38.5 Radius 0 Mid- 143 205 48 126 159 **  16* 145.6 32.7  49.9 Radius 0 Avg 142 204 25 47 124 155 155   30    44 1027 Mid- 171 215 25 40 19 142 164 17 16 160.2 36.1  54.5 Radius 1027 Mid- 168 213 26 42 23 162.1 27.2  52.0 Radius 1027 Center 143.1 38.1  48.9 1027 Surface 107.5 30.1  60.2 1027 Surface 108.6 39.2  60.9 3000 Mid- 162 212 22 35 12 142 163 23 24 140.1 37.9  60.9 Radius 3000 Mid- 163 212 22 35 12 141 162 25 31 138.1 41.8  61.8 Radius 10000 Mid- 145 206 18 21 118 154 34 67  49.7 33.0  66.6 Radius 10000 Mid- 143 206 16 17 118 154 36 67  37.3 36.4  68.0 Radius 1027 Avg 169 214 26 41 21 142 164 17 16 161   32    52 Ratio   119%   105%  103%   86%   115%   106% — — 104% 105%  120% 3000 Avg 163 212 22 35 12 142 163 24 28 139   40    61 Ratio   115%   104%   89%   74%   114%   105% — —  90% 132%  139% 10000 Avg 144 206 17 19 118 154 35 67 44  35    67 Ratio   84%   96%   65%   48%   83%   94%  207%  419%  27% 96% 123% 10932 0.39 0 Mid- 177 217 22 36 146 168  6  7  86.0 27.9  38.8 Radius 0 Mid- 177 217 22 36 124 161  7 11  83.5 ** ** Radius 0 Avg 177 217 22 36 135 165  6  9 85  28    39 1027 Mid- 171 216 17 23 9 142 164 10  8  72.7 17.9  17.5 Radius 1027 Mid- 172 216 19 25 9  70.2 18.8  16.8 Radius Center  59.0 13.1  15.8 Surface  53.8 40.3  54.9 Surface  60.8 20.2  19.9 3000 Mid- 165 214 17 22 6 140 162 17 23  66.7 24.0  21.0 Radius 3000 Mid- 169 217 17 24 6 138 161 16 16  68.7 41.8  43.1 Radius 10000 153 208 14 16 114 151 34 58  27.0 37.9  68.0 152 207 13 13 115 151 26 45  24.7 38.3  67.9 1027 Avg 171 216 18 24 9 142 164 10  8 71  18    17 Ratio   97%   100%   81%   67%   105%   100%  156%   88%  84% 66%  44% 3000 Avg 167 216 17 23 6 139 161 17 20 68  33    32 Ratio   95%   99%   78%   65%   103%   98%  261%  209%  80% 118%   83% 10000 Avg 153 208 13 14 114 151 30 51 26  38    68 Ratio   86%   96%   60%   40%   84%   92%  472%  546%  31% 137%  175% * = broke in outer portion of gage section; ductility may not be representative ** = broke at gage mark; ductility values are not valid Heat Treatment: 1800° F. + aged 1450° F./8 h/FC to 1300° F./8 h/AC Specimens: Tensile - 0.250″ gage diameter threaded, low-stress ground Stress Rupture - 0.178″ diameter combination smooth and notched (Kt = 3.9), low-stress ground 

1. A method of making a precipitation hardenable nickel base alloy comprising the steps of: providing charge materials in a vacuum melting furnace, said charge materials being selected to provide a precipitation hardenable nickel base alloy; adding to said charge materials an amount of silicon effective to provide precipitation of a globular intermetallic phase in the alloy during elevated temperature processing thereof; melting said charge materials and additions to form said alloy; and then casting the molten alloy to form an ingot.
 2. A method as set forth in claim 1 wherein the step of providing the charge materials comprises the step of providing charge materials selected to provide a composition containing, in weight percent, about Carbon 0.10 max. Manganese 0.35 max. Phosphorus 0.03 max. Sulfur 0.015 max. Chromium 12-20 Molybdenum 4 max. Tungsten 6 max. Cobalt 5-12 Iron 14 max. Titanium 0.4-1.4 Aluminum 0.6-2.6 Niobium 3-7 Boron 0.003-0.015

the balance being nickel and usual impurities.
 3. A method as set forth in claim 2 wherein the step of adding silicon comprises adding sufficient silicon to provide a retained amount of about 0.2% to about 0.7% silicon in the ingot.
 4. A method as set forth in claim 1 or claim 2 comprising the steps of: forming said ingot into an article; solution treating said article at a temperature of about 1750-1850° F.; and then age hardening said article.
 5. A precipitation hardenable nickel base alloy that provides a unique combination of elevated temperature strength and ductility with reduced notch sensitivity at temperatures up to about 1300° F., said alloy comprising, in weight percent, about Carbon 0.10 max. Manganese 0.35 max. Silicon 0.4-0.7 Phosphorus 0.03 max. Sulfur 0.015 max. Chromium 12-20 Molybdenum 4 max. Tungsten 6 max. Cobalt 5-12 Iron 14 max. Titanium 0.4-1.4 Aluminum 0.6-2.6 Niobium 3-7 Boron 0.003-0.015

the balance being nickel and usual impurities.
 6. An alloy as set forth in claim 5 which contains at least about 4% niobium.
 7. An alloy as set forth in claim 5 or claim 6 which contains not more than about 0.6% silicon.
 8. An alloy as set forth in claim 7 which contains not more than about 6% niobium.
 9. An alloy set forth in claim 8 wherein the sum of molybdenum and tungsten is at least about 2% and not more than about 8%.
 10. An article formed of a precipitation hardenable nickel base alloy as claimed in claim 5 comprising a matrix formed of a nickel base alloy, a strengthening precipitate dispersed in said matrix, and a globular intermetallic precipitate dispersed at grain boundaries of said matrix material, such that the globular intermetallic precipitate restricts grain growth during elevated temperature processing of the alloy.
 11. An article as set forth in claim 10 wherein the globular intermetallic precipitate contains one or more of Si, Fe, Ni, Co and Cr, or a combination thereof, in combination with one or more of Nb, Mo, W, and Ti, or a combination thereof.
 12. An article as set forth in claim 10 which has been solution treated at a temperature of about 1750-1850° F. and age hardened.
 13. An article as set forth in claim 10 which has been solution treated at a temperature of about 1800-1850° F. and age hardened. 